Can You Overdose on Vitamin C?

This is a common question and people seem to be confused about it, as many respected individuals advocate huge doses of vitamin C. Truth be told, vitamin C is relatively non-toxic, probably the less toxic of all vitamins, along with some B vitamins. However, there are some studies that suggest too much of it is possibly linked with an increased prevalence of kidney stones. Vitamin C is metabolized to a urinary product called oxylate, and guess what, many kidney stones are oxylate-based. In these clinical trials individuals are consuming 1000 milligrams a day or more, much more than what you can get from “natural” foods (not supplements).

In individuals with iron deficiency, taking up to ten times the recommended amount (the recommended is about 90 milligrams daily) can destroy significant amounts of vitamin B12. In healthy people, excess vitamin C can cause bowel irritation (diarrhea).

Diarrhea may not seem like something serious, but there is another really disconcerting consequence of taking too much vitamin C: it can interfere with diagnostic tests. For example, if the doctor is trying to know if you’re a candidate for colonoscopy or not, a lot of vitamin C can actually interfere or react with the agent that is testing for blood. You should tell your doctor if you’re taking any vitamin supplement.

Vitamin C can also interfere with the test for glucose or sugar in your urine. It can show that you have sugar in your urine when you don’t. As a rule of thumb, keep the vitamin C intake below 2000 mg. This is really a huge number, so don’t worry if you’re not eating supplements like candy.